Flexdex™: A Minimally Invasive Surgical Tool With Enhanced Dexterity and Intuitive Control

The goal of this project is to develop a low-cost minimally invasive surgery (MIS) device that provides wrist-like dexterity and intuitive control, which are necessary for complex MIS tasks such as suturing, knot-tying, and fine dissection. Such functionality is currently available only in multi-million dollar surgical robots. The proposed technology will broaden the adoption of MIS procedures by dramatically lowering the technology cost as well as surgeon training burden, thus extending the benefits of MIS to a larger portion of the population.

The proposed FlexDexTM device concept employs two major innovations that represent a fundamental paradigm shift in the physical configuration of hand-held, mechanical tools: 1. We create a mechanism around the surgeon’s wrist that geometrically projects a ‘virtual center’ of rotation at the wrist. Thus, no physical structure need exist at the surgeon’s wrist. 2. This ‘virtual center’ mechanism is placed between the tool handle and a tool frame, which is now attached to the surgeon’s forearm via an arm-brace. These innovations result in several unique and desirable attributes. Mounting the tool frame provides a direct transmission of the three translations and roll rotation of the surgeon’s forearm to the tool shaft and end-effector. Independent of these 4 DoF, the two wrist rotations of the surgeon’s hand are captured by the virtual center mechanism and transmitted to the end-effector via transmission strips, pulleys and cables. Thus, while the surgeon’s wrist is allowed to rotate freely and naturally, these two wrist rotations are effortlessly transmitted to the transmission pulleys. A cable-based system is then used to further transmit these rotations to the end-effector, providing another two DoF.

Preliminary results
To generate a preliminary confirmation of the effectiveness of this innovation, we have developed a concept prototype and sought feedback from a group of surgeons. This prototype demonstrates that in the FlexDex device, when a single rotation (e.g. up/down) is needed at the end-effector, the surgeon only provides an analogous up/down hand rotation about his/her wrist. During this action, his shoulder, elbow, and forearm remain at rest, with the latter aligned with the tool shaft. This intuitive one-to-one mapping between the surgeon’s input motions and the end-effector output motions makes the FlexDexTM tool a natural extension of the surgeon’s forearm and hand. Furthermore, its cable-based mechanical transmission relays the forces exerted by the end-effector back to the surgeon’s hand to provide a natural ‘feel’ during surgery. Additionally, the reaction forces at the surgical port appear to be all but eliminated.

Conclusions/future directions.
The FlexDexTM concept has shown considerable early promise. We are now proceeding with design, and fabrication of at least two pre-clinical prototypes of the above described FlexDexTM tool concept. These prototypes will fully embody the mechanical functionality claimed earlier, including enhanced dexterity and grasping action (i.e. seven DoF) and intuitive control. These prototypes will be tested in a simulated clinical environment completing representative advanced MIS tasks to validate the technology in comparison to standard and robotic surgical instruments.

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